The invention relates to an apparatus, and method of utilization thereof, primarily adapted for the mixing of chemicals in suspensions, such as mixing bleaching fluids (liquid or gas) in cellulosic fiber suspensions (particularly paper pulp).
According to the present invention, a mixing apparatus is provided that is capable of efficiently mixing chemicals with suspensions over a wide variety of suspension solids concentrations, and which is compact, simple, and relatively inexpensive. The apparatus according to the present invention is capable of efficient mixing of chemicals with pulp having a concentration range of about 2-15%, and preferably about 8-14%. The apparatus is operated in such a manner that fluidizing of the pulp is effected during mixing, and the total residence time within the mixing apparatus is considerably shorter than in conventional mixing apparatus (e.g., about 0.01-2.0 seconds, preferably 0.05-0.5 seconds).
The mixing apparatus according to the present invention comprising a housing having a first cylindrical housing part, and a second cylindrical housing part with a larger diameter than the first part. The housings are connected together so that the cylindrical axes thereof are substantially coextensive and so that the interiors thereof are in communication. A fluid inlet means is provided to the housing first part for introducing fluid axially into the first housing part, and a fluid outlet means is provided from the second housing part for expelling treated fluid tangentially from the second housing part. Treatment fluid inlet means introduces treatment fluid to the housing at one or more locations, preferably both in the first housing part and the second housing part.
The apparatus according to the invention further comprises means for effecting stirring of the suspension and mixing of treatment fluid with the suspension. Such means includes a shaft, means for mounting the shaft for rotation with respect to the housing about an axis substantially coaxial with the axes of the housing first and second parts, and first and second stirring members operatively mounted to the shaft and extending in the first and second housing parts, respectively. The first stirring member has a plurality of substantially axially extending, radially upstanding ribs formed on the axial periphery thereof, which cooperate with a plurality of radially spaced substantially axially extending, radially upstanding ribs formed on the interior of the first housing part. The second stirring member has a plurality of substantially radially extending axially upstanding ribs formed on a peripheral surface thereof, and cooperating with a plurality of axially spaced radially extending, axially upstanding ribs formed on the interior of the second housing part. A drive effects rotation of the shaft so that the stirring members fluidize the suspension, while the residence time of each increment of suspension is about 0.01-2.0 seconds.
According to the method of mixing treatment fluid with a suspension utilizing the apparatus heretofore described, a suspension having a solids consistency of about 2-15% (preferably 8-14%) is introduced axially into the first housing part. Treatment fluid is introduced into the suspension flowing in the first housing part to be mixed with the suspension, and suspension mixed with treatment fluid is withdrawn from the outlet. The first and second stirring members are rotated with respect to the housing at a speed sufficient to effect fluidization of all of the introduced suspension and to effect transport of the suspension from the inlet, past the ribs associated with the housing first and second parts and the first and second stirring members which effect mixing of the treatment fluid in suspension to the suspension outlet, providing a residence time within the housing of each increment of suspension introduced into the inlet of about 0.01-2.0 seconds (preferably 0.05-0.5 seconds). Chlorine and chlorine dioxide may be utilized as the treatment fluid, or oxygen may be utilized as the treatment fluid introduced radially into the first housing part, with an alkaline solution introduced at a peripheral point generally parallel to the axis of the housing parts into the second housing part.
It is the primary object of the present invention to provide a simple yet effective apparatus and method for mixing a fluid with a treatment fluid, particularly for mixing treatment fluids in high consistency suspensions. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claim.